The main focus of this thesis has been the activity development of social work practice. The thesis presents the construction of a theoretical frame for developing social work practice; namely, Interactive Activity-Documentation model (IAD), and includes the process of testing and reviewing the model.The thesis was based on an interactive research design, which involved the researcher and the practitioners in the development and testing of the model. The researcher constructed the IAD model based on theoretical considerations concerning the characteristics of social work, the practice’s knowledge requirements, learning processes, reflexivity in relation to actions, the systematic documentation of actions and reflections and the need for an interactive process to enhance the usage of the model.The setting in which the testing and the development of the model took place was a family centre, an organization in which a social worker, a midwife, paediatric nurses and preschool staff work together to coordinate services for families with children. The material that was used during the testing and for the review of the model consisted of descriptions of the family center’s aims, goals and objectives in a foundation document, continuous descriptions and reflections of the practitioners’ actions, descriptions and reflections of how the families understand the practice, documents in which the content of the foundation document and the continuous descriptions and reflections from the practitioners and families are compared and notes from the practitioners’ discussions about the comparison.The study showed that the use of a model for activity development in social work practice provides the practitioners with the possibility to systematize their documentation and the tools that they use in the development process. Another finding in the study was the importance of dealing with explicit assumptions in the construction process. Explicit assumptions provide the opportunity to discuss the possibilities of the model and potential problems. The staff’s critical discussions concerning the resources of the organization revealed that, for example, time spent together with other staff members had a positive impact on the development process. The review also shows that development achieved by learning through reflection enhances critical thinking in social work practice.